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How to Connect a Car Subwoofer to an Old Amplifier?

If you’re looking to add some extra thump to your car audio system, you might be wondering how to connect a car subwoofer to an old amplifier.

Connecting a subwoofer to the old amplifier is not much different from connecting it to the new amp. Connect the speaker outputs on the amplifier to the matching inputs on the subwoofer using a speaker wire, ensuring the polarity is correct.

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Tip: You will also need to check the settings on your amplifier to ensure that it is configured for use with a subwoofer and it has matching impedance. Additionally, you may want to adjust the gain and frequency levels to get the best sound from your new setup.

If your car amp is really old and is not equipped with any filters or adjustments, you may need to consider purchasing a new amp for the subwoofer.

The best effect you will get from the monoblock type amp, for example Skar (link to Amazon).

In this article, I will cover subwoofers in-depth, detailing the principle that allows them to work correctly, their different types, and how to set them up to your old car amplifier.

Factors to consider when connecting car subwoofers to your old car amplifier.

Before we dive right into this tutorial, there are a few factors that you need to consider and have in place before we proceed, and we will cover them here.

how to connect subwoofer to old amplifier

Pre-setup required to connect car speakers to car amplifiers.

In this tutorial, I assume that your car is already configured and set up with an amplifier. I will focus only on connecting subwoofers to existing old car amplifiers.

Your amplifier should be set up and wired so that it draws power from your battery and is earthed using a ground wire to a section of your car.

Old amplifiers will most likely not have remote detection; however, if your amplifier does, it should also be wired to your car stereo to turn on automatically. 

Factory stereo has speakers wire, so you need a converter to run to the amp with RCA; use a line output converter (crossover) (convert speakers wire into RCAs). 

Any additional steps and measures also should be implemented, such as using Fexlume for your wire and having fuses installed in the correct locations. 

Required components

The only additional component that is required is a crossover (line output converter). You will only need to purchase one if your active or passive subwoofer does not have a built-in crossover. For the most part, all modern active subwoofers will include built-in crossovers that you will be able to adjust. 

A passive subwoofer may not have a crossover built into it. Therefore you will use this device and insert it between your subwoofer and old amplifier, enabling the separation of low frequencies that will be sent to your subwoofer.

Required tools

To install your subwoofer, no matter if it is active or passive, you will need some of these parts and tools, depending on the configuration of your setup.

  • Subwoofer speaker (active or passive)
  • Subwoofer enclosure (box)
  • Your old car amplifier
  • Wiring kit (if you do not have any parts, fittings, or cables)
  • RCA cables the amount you need will depend on the configuration)
  • Speaker wire
  • RCA to speaker wire cables
  • Basic tools like a screwdriver, wrench, etc.

Connecting your subwoofer to an old car amplifier

One thing to note is that connecting your subwoofer to your amplifier will be straightforward. The complications will come in when determining connection types on your amplifier and if your subwoofers have crossovers built into them or not. 

How to connect a passive subwoofer to an old amplifier?

Assuming your old amplifier does not have a built-in crossover, it is essential to know what output connection types it has for speakers. Your amplifier will either have terminals for standard speaker wire or RCA connections. Sometimes it will have both.

The next thing we need to determine is if your passive subwoofer has a built-in crossover. 

Once you know what these factors are, you can continue with two scenarios:

The first scenario is that your passive subwoofer does not have a built-in crossover. The method then is to purchase a passive crossover and then set it between your subwoofer and amplifier. 

Depending on what connection types your amplifier has, you can either use an RCA cable and run it to your crossover or use a speaker wire to an RCA cable and run it to the crossover. 

Then you would need to use an RCA to speaker wire cable connecting the crossovers to your subwoofer. The crossover adapter will allow you to adjust the bass and gain the subwoofer levels according to your taste. 

How to connect an active car subwoofer to an old amplifier?

Active care subwoofers (subwoofers that have a built-in amplifier) are trickier in terms of understanding high and low-level audio signals, not the process of connecting them.  

Understanding how high and low-level audio works is not important right now. However, knowing what connections to use are. 

Remember that your amplifier is a source of power, so is the amplifier in your active subwoofer. It is not recommended that you link your amplifier and active subwoofer via high-level audio signals. You would need to have an active subwoofer that offers RCA input connections.

Because your active subwoofer will most likely have a built-in crossover, you will not need to purchase the external passive adapter. All you would need to do is run a wire, preferably from your amplifier’s RCA outputs if they have, into your subwoofer’s low-level RCA inputs.

If your amplifier only has terminals to connect standard speaker wire, then you would need to use a speaker wire to RCA cable as in the above example.

How to connect a subwoofer to an old car amp without sub out?

If you are lucky enough to have an amplifier with five channels and one channel is a dedicated subwoofer output, this is the most optimal setup. The amplifier will have a crossover built-in to it, and the same principles apply as for the previous methods. 

If you have a passive speaker, all you would need to do is run speaker wire from the dedicated subwoofer channel on your amplifier to your subwoofer. 

If you have an active speaker and your amplifier supported low-level RCA outputs, all you would do is run an RCA cable from your amplifier to the RCA inputs on your active subwoofer. However, if your amplifier only supported terminals with standard speaker wire, you would need to use a speaker wire to RCA cable and run that into the RCA inputs of your active subwoofer.

Subwoofers overview

Subwoofers are a big part of car audio, and a car audio system is not complete without them. There are a few features that modern subwoofers have, and there are two types. If you don’t know what kind of subwoofer you have and you don’t know if it sports the feature you need to connect it to your old car amplifier, this initial section will cover it.

Frequency design

Subwoofers are not like regular speakers. They are designed to produce and enhance low bass frequencies giving your audio depth and thickness. 

The way subwoofers can do this and how other pieces of audio equipment can help you obtain this effect is by a crossover. 

Audio crossover is a type of electronic filter circuitry that allows for the isolation and adjustment of specific frequencies, in this case, low frequencies. Subwoofers utilize this type of technology to only play bass frequencies and thus can enhance the audio quality.

Subwoofers can have built-in crossovers in the form of passive circuitry and active circuitry. Other audio equipment can also have crossovers built into them, such as amplifiers. Depending on your type of subwoofer, it may or may not employ this type of circuitry, and therefore we need to find other means in terms of getting them to function correctly.

Passive subwoofers

Passive subwoofers are simply a subwoofer speaker that sits inside its enclosure (box, and sometimes referred to as a bin). They need to be powered by an external source, increasing the speaker’s low-level signal passed line-level enabling it to boost the sound. This source is your powered amplifier. 

Passive speakers, including subwoofers, will usually have one connection type, which are standard terminals that utilize speaker wire. 

One thing to note is that most passive subwoofers will have a passive bass crossover installed within the speaker and will be wired directly to the terminal for external connecting. Therefore you will not need to purchase an additional crossover; however, if your subwoofer does not have a passive bass crossover built within it, you will have to buy this as an extra addon. 

Remember that if you connect your subwoofer to your amplifier without crossover, the sound will be nothing short of horrific. When talking about crossovers, you can install a simple crossover that will add a boost to your bass, or if you need more customized settings, reach for the fantastic AudioControl LC2i 2 Channel Line Out Converter with AccuBASS and Subwoofer Control.

Active subwoofers

Active subwoofers have a built-in amplifier and will usually have one or more input connection types. They will typically have speaker inputs (standard speaker wire) RCA inputs, and then with today’s modern amplifiers, some will even come with digital audio connections in the form of S/PDIF.

The low-level signal from the active subwoofers will be boosted dramatically, utilizing the built-in power amplifier and crossover.

For the most part, when working with powered subwoofers, you will use the available RCA connections unless a situation arises that requires you to use standard speaker wire and terminals.

Car amplifiers overview

A car amplifier works on the same premise as any other powered audio amplifier, increasing a low-level signal or line-level signal, allowing it to drive loudspeakers so we can listen to music at loud volumes if we so wish to.

Car amplifiers had come a long way from when they were first introduced and become popular in the 90s’. 

Features of a modern car amplifier

We will briefly discuss modern car amplifiers. If you ever feel like you would want to upgrade your old amplifier to a new one after completing the tutorial below, knowing what features they have compared to old car amplifiers will help you decide which one to purchase. 


Modern amplifiers now come with five channels (four channels for the speakers and one channel dedicated for the subwoofer). Older amplifiers had the capacity of four channels, and individuals used this set up to drive the front and rear speakers, with the amplifier bridged to drive a subwoofer.

Modern car amplifiers also provide more power sent to the subwoofer channel ranging from 300 to 600 watts, while the four main channels receive 50 to 100 watts.

In addition to an extra subwoofer channel, because the subwoofer channel is built as part of the amplifier, it reduces the need for power and ground distribution blocks. A fantastic example of the five-channel amplifier is the BOSS Audio Systems PV3700.


Crossovers are another part of the features that are common in the new amplifiers, negating the need to purchase an additional crossover as extra equipment.

Most new amplifiers with four channels will likely support crossovers that you can manually configure in low-pass or high-pass mode. A great example of an amplifier with a built-in crossover is Audison SRV.

OEM and remote detection

OEM is the sound system that comes standard with your car. Modern amplifiers require OEM integration because sometimes the factory source unit cannot be replaced.

Using older amplifiers will not be a problem because, practically, they just amplify the sound. However, with DSP (Digital Signal Processing) becoming more prevalent, modern amplifiers need a way to compensate for this.

These features include the amplifier being able to accept speaker-level signals (dedicated connections for high-voltage signals or RCA connections with a button allowing you to reduce voltage).

Another feature of modern amplifiers is their ability to detect when the car stereo is turned on, and then it will power on automatically. With older amplifiers, you have to switch them on.

A great example of a four-channel car amplifier with built-in OEM is Massive Audio Blade BP800.4.


DSP is becoming more common in today’s digital world. Simply put, the DSP system manipulates audio signals to achieve specific goals like negate road or engine noise and make audio more clear, crisp, and definitive.

Benefits are clear, and DSP is really needed feature if you are continually opting for better and more clear car audio quality. An outstanding sound quality offers Sony XM-GS6DSP.

Remote level controls

The function of turning the bass up or down is another great feature, and modern car amplifiers have this. 

It is usually a plastic or metal box with a level knob on it to control your subwoofer. Older car amplifiers might have had bass knobs, but you would either have to stop the car, get out and manually adjust the bass from the trunk or hatch.

In other cases, if you did not want to do this, you would have to change the bass before driving and leave it set to that level. I remember my first amplifier MacAudio did not have this option, and constant adjustments were really annoying.

I wish I had by then something like BOSS Audio that can make listening to the music while driving really enjoyable.

Some amplifiers come with attenuators, and some come with bass boost controls.

Many car audio enthusiasts believe that attenuators are better (the standard bass level is set at maximum volume, and you can only adjust it lower). This is because good sound systems are tuned well, and boosting the bass is considered overkill and could mess with the sound.

Old car amplifiers vs. new car amplifiers

Although both are precisely the same in principle (their primary purpose is to amplify an audio signal), a few features and aspects separate new car amplifiers from old ones. We will discuss three of them.


Many car audio enthusiasts prefer old car amplifiers because they bring back great memories of when car audio became popular and mainstream. This is not a tangible aspect of a car amplifier’s power or quality, but it is definitely true. 

You will often see car audio enthusiasts sorting after and collecting car amplifiers from way back when as a hobby, just like car enthusiasts collect vintage cars.

Check out this video by Willston Audio labs and their incredible collection of old-school car amplifiers.

Build quality

Car amplifiers that were produced in the early days were built to last for a long time and made from materials that can stand time and weather from the elements. This does not mean that modern car amplifiers are not built to last or are made of low quality, but something is missing. There is no personality, no heart added, just electronics. 

Contrary to that, modern car amplifiers are made with better technology, which includes built-in DSP, equalizers, and crossovers. They are made from cheaper parts and materials (not necessarily of lower quality), offer more power and lower current draw, and therefore, you can get more bang for your buck.

Old amplifiers are just built with a more solid feel to them using more solemn and more expensive materials, and some car audio enthusiasts, including me, like this so much.

Features and functions

As we now know, the features of newer amplifiers can be extensive and range more amplifier channels, built-in crossovers, vehicle integration features, remote level controls, more amplifier power, integrated DSP, and more.

Although these features may appeal to modern car audio enthusiasts, some individuals prefer just having two and four channels with simple bass and treble controls.

It provides a sense of simplicity and a hassle-free mindset (not worrying about hundreds of wires and different features).


This article went into depth about subwoofers, the circuitry involved in making them able to function correctly, the different types of subwoofers, and how to connect these different types to your old car amplifier. 

We also went into depth about old and new amplifiers discerning similarities and differences between them. Understanding this can give us a clear picture of how they work and function together with a subwoofer. 

Hence, understanding this allowed us to connect and configure any type of subwoofer to an older car amplifier.